The invention relates to a semiconductor device having a field effect transistor and comprising a semiconductor body having a stack of, in succession and viewed from the upper surface of the semiconductor body, a first semiconductor region of a first conductivity type, which forms a source of the transistor and is provided with a first connection conductor, a second semiconductor region of a second, opposite conductivity type, and a third semiconductor region of the first conductivity type, which forms a drain of the transistor and is provided with a second connection conductor, and a gate which laterally adjoins the second semiconductor region, by means of which gate a current can be sent between the first and the third semiconductor region and through the second semiconductor region, and which comprises a gate electrode, with the first connection conductor and the gate electrode being connected to, respectively, a first and a second connection region situated on the upper surface of the semiconductor body. Such a device is used, in particular, as a power transistor in, for example, an electronic power supply. Although such a transistor is often considered to be a discrete component, in practice a plurality of other electronic components are often integrated in the semiconductor body. The invention also relates to a method of manufacturing such a device.
A device of the type mentioned in the opening paragraph is known from United States patent specification U.S. Pat. No. 5,883,411, published on Mar. 16, 1999. In said specification, a description is given of a transistor having an n+ type substrate provided with an nxe2x88x92 type epitaxial layer, which form the drain, and a p-type epitaxial layer, which forms a channel region and wherein an n+ type diffusion region is locally present which forms the source of the transistor. In the upper surface of the transistor there is a groove whose wall is covered with an insulating layer, forming the gate oxide, on which the gate electrode is present, which jointly form the gate of the field effect transistor. Source and drain are provided with a connection conductor. The connection conductor of the source, and a part of the gate electrode jointly form a connection region at the upper surface.
A drawback of the known device resides in that it is comparatively bulky because the device is intended, in particular, for power applications. Even for a component that is considered to be a discrete component, the device is comparatively large, which can be attributed to the fact that, in practice, often a number of additional components are still integrated jointly with the transistor.
Therefore, it is an object of the invention to provide a device which is comparatively small and which, in addition, can be economically manufactured.
To achieve this, a device of the type mentioned in the opening paragraph is characterized in accordance with the invention in that the semiconductor body is provided with a though-hole at least one wall of which is covered with a conductive layer, which is connected to the third semiconductor region and which forms the second connection conductor and is connected to a third connection region situated on the upper surface of the semiconductor body. The invention is based on the recognition that the size of the known device can be reduced comparatively substantially if the protective coating of the transistor and the space necessary for final assembly can be decreased. By providing the semiconductor body with a through-hole the wall of which is covered with a conductive layer, which is connected, on the one hand, with the drain situated on the lower side and, on the other hand, with a connection region situated on the upper side, also the drain of the transistor can be contacted at the upper side. As a result, the device in accordance with the invention can suitably be used for surface mounting and hence both the protective envelope and the space necessary for final assembly can be substantially reduced. The invention is further based on the recognition that such a through-hole can be made very readily and economically, for example by means of laser cutting or sandblasting, and that the conductive layer can be insulated with respect to the channel region in a very simple manner, and that a connection between the conductive layer and the drain can be very readily obtained. As a result, a device in accordance with the invention is not only very small but also inexpensive, which can be partly attributed to the fact that money is saved on the envelope. Preferably, the conductive layer is a metal layer.
In a preferred embodiment of a device in accordance with the invention, the connection regions on the upper surface are provided with means for surface mounting the semiconductor body, said means preferably comprising an array of spherical conductors. In this manner, the advantage of the invention is exploited in full. The device is then secured, for example by means of soldering, onto a support plate provided with a conductor track, for example a PCB (=Printed Circuit Board), with the upper side of the semiconductor body facing the support plate.
In a further very favorable modification, the second semiconductor region comprises a semiconductor substrate wherein, at the upper side and the lower side, respectively, the first and the third semiconductor region are formed by means of diffusion or ion implantation. This modification is connected with an important additional advantage of a device in accordance with the invention. Namely, by using a through-hole, the thickness of the semiconductor body no longer matters, in principle. As a result, the device in accordance with the invention can very suitably be used when the second semiconductor region is a very thick epitaxial layer or even a substrate. The use of a substrate has the important advantage that epitaxy, which is relatively expensive, is superfluous. In addition, the transistor of this modification can very suitably be used at high voltages, which is an important advantage because a high dissipation often involves not only a high current but also a high voltage.
Using the above-mentioned techniques, such as sandblasting or laser cutting, a round through-hole can be readily made. This has the advantage that the semiconductor body is weakened as little as possible by the through-hole. In this case, preferably all walls of the through-hole are covered with the conductive layer, so that the connection resistance of the drain is as low as possible. The through-hole (or the through-holes) may be situated between the various components of the transistor or even within the active region of a (sub-)transistor. (In the latter case) there is preferably an insulating layer or a so-called guard ring in or around the through-hole, at least between the conductive layer and the second semiconductor region, to preclude short-circuits. If the guard ring comprises a doped region, said guard ring does not have to be directly adjacent the walls of the through-hole.
In an important embodiment, the through-hole is slit-shaped. If all the walls of the through-hole are, at least substantially, covered with the conductive layer, then the connection resistance of the drain is very low. If the slit-shaped through-hole is positioned between two neighboring transistors, the through-hole can be xe2x80x9csharedxe2x80x9d by the two transistors. In this case, the hole is positioned, for this purpose, in the middle of the scratch or saw path which serves to separate two individual transistors from each other. As a result, the term xe2x80x9cthrough-holexe2x80x9d is to be taken to include also, in this application, a recess in a side face of the semiconductor body, which recess extends across the entire thickness of the semiconductor body. Owing to the elongated shape of the through-hole, the drain of the transistor of this modification can still have a very low connection resistance in spite of the fact that the through-hole is shared by two neighboring transistors. This still applies if the end faces of the slit-shaped through-hole are not provided with a conductive layer. This has the important advantage that positioning the slit-shaped through-hole in (the center of) a scratch or saw path does not lead to additional problems because, during sawing the semiconductor body, a saw blade does not have to saw through the conductive layer.
A method of manufacturing a semiconductor device having a field effect transistor and comprising a semiconductor body in which, viewed from the upper surface of the semiconductor body, a stack is formed of a first semiconductor region of a first conductivity type, which forms a source of the transistor and is provided with a first connection conductor, a second semiconductor region of a second, opposite conductivity type and a third semiconductor region of the first conductivity type, which forms a drain of the transistor and is provided with a second connection conductor, and a gate which laterally adjoins the second semiconductor region, by means of which gate a current can be sent between the first and the third semiconductor region and through the second semiconductor region, and which comprises a gate electrode, with the first connection conductor and the gate electrode being connected to, respectively, a first and a second connection region situated on the upper surface of the semiconductor body, characterized in accordance with the invention in that the semiconductor body is provided with a though-hole at least one wall of which is covered with a conductive layer, which is connected to the third semiconductor region and which forms the second connection conductor and is connected to a third connection region situated on the upper surface of the semiconductor body. In this manner, a device in accordance with the invention is obtained in a simple manner. In a preferred embodiment, the through-hole is slit-shaped and positioned next to the transistor at the location of a scratch or saw path, and the conductive layer is formed on the two walls of the through-hole which extend in the longitudinal direction. As a result thereof, the through-hole can be shared by two neighboring transistors and, in addition, across the through-hole a partition can be made, if necessary, to separate two neighboring transistors. In this case, preferably, first all the walls of the through-hole are covered with the conductive layer, after which the walls of the through-hole and the surface of the semiconductor body are covered with a photoresist which is exposed, said photoresist being provided with a mask at the location of the end faces of the through-hole,(said mask being a spot in the case of a negative photoresist and an aperture in the case of a positive photoresist), whereafter the conductive layer on the end faces of the through-hole is removed by means of etching.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.